1. Field of the Invention
The present invention generally relates to the interconnection of optical devices and optical media, and more particularly to a method of passive self-alignment of an array of active optical devices (e.g., laser drivers and photodetectors) to a corresponding array of optical fibers. The method also allows for the integration of other electronic components, such as amplifier drivers, in the interconnection.
2. Description of Related Art
Optical fibers have replaced copper wire in recent years as the preferred medium for carrying telecommunications and data signals, due to the high efficiency of optical data transmission. As with copper wire, it is necessary to provide for the interconnection of optical fibers, during installation, repair or replacement of the fibers, and to terminate the fibers onto active optical devices.
Optical devices include, for example, optical sensors (photoelectric diodes or photodetectors) and light sources (typically solid-state devices, such as light-emitting diodes (LEDs) or laser diodes). The termination of an optical fiber may be indirect, i.e., the fiber may be connected to some other (passive) optical device such as a beam splitter or polarizer, before the light beam is directed to the active optical device.
There are generally two kinds of optical interconnection devices, splices and connectors. The term xe2x80x9csplicexe2x80x9d usually refers to a device which provides a permanent connection between a pair of optical fibers (i.e., a connection that is not intended to be removable). Many fiber optic splices employ plate elements having fiber-receiving V-shaped grooves, with means provided for clamping the terminal ends of a pair of fibers in a common groove. Some of these devices are designed to interconnect a plurality of pairs of fibers; see, e.g., U.S. Pat. No. 5,151,964.
The term xe2x80x9cconnector,xe2x80x9d in contrast, usually refers to a device which may be engaged and disengaged repeatedly, often between different plugs and receptacles. Connectors also can be used to removably interconnect a plurality of pairs of fibers; see, e.g., U.S. Pat. No. 5,381,498. The present invention is generally related to such devices, although the term xe2x80x9cconnectorxe2x80x9d should not be construed in a limiting sense, since the present invention may inherently provide a permanent, as well as temporary connection/termination.
There are two primary types of commercially available fiber optic connectors, namely, ferrule connectors and bionic connectors. Ferrule connectors use a ferrule plug, typically ceramic, having a central bore which receives a single optical fiber. Bionic connectors use a plug in the shape of a truncated cone. Both connectors usually combine a pair of plugs fitting into a common socket or receptacle to provide a completed connection. The prior art includes hybrid ferrule connector/splices, such as those shown in U.S. Pat. Nos. 4,986,626 and 5,159,655.
One area which has not been adequately addressed by the prior art, however, is the interconnection, or termination, of an array of optical fibers to a corresponding array of active optical devices. Since the plugs of ferrule and bionic connectors receive only a single fiber, a relatively large bank of such connectors must be provided to terminate several fibers. One drawback with multifiber connectors is the poor interconnection densities that are achieved. While some ferrule designs have densities around 2 connections per square centimeter, this may be compared to densities of 4 connections or more per square centimeter in some copper wire connectors, such as an RJ45 connector. Some non-ferrule designs provide slightly improved densities, such as that described in U.S. Pat. No. 4,045,121, but that connector has far too many parts and is not easily installed. A simpler multifiber connector is depicted in European Patent Application No. 514,722 (commonly referred to as an xe2x80x9cMTxe2x80x9d connector).
Fiber alignment is also a problem when terminating an array of fibers at respective optical devices. Each fiber must not only be properly aligned transversely, i.e., with the fiber tip precisely located at the emitter or receiver of the active device, but must further be positioned in the proper angular orientation to ensure that the light beam exits/enters the fiber in an optimum direction with respect to the device. Any air gap between the endface of an optical fiber and the optical surface of a respective active device should also be minimized in order to reduce transmission losses across the interface. Accurate alignment of fibers with active devices is thus a tedious and time-consuming process.
In order to discover the best position/orientation, active alignment techniques detect actual transmission of optical signals across the device-fiber interface. For optical sensors, active alignment is accomplished by transmitting a signal through the fiber to the sensor, and then monitoring the sensor output while moving the terminal end of the fiber, or other alignment element. The signal can be fed into the other (distal) end of the fiber, or injected at an intermediate point using a xe2x80x9cclip-onxe2x80x9d instrument that creates a microbend in the fiber at the injection point.
For light sources, active alignment is accomplished by powering up the device, and then monitoring the signal that flows though the fiber while moving the terminal end of the fiber or other alignment element. The signal can be monitored by sensing the output at the distal end of the fiber, or by picking the signal off at an intermediate point using a clip-on instrument. For either type of optical device (transmitter or receiver), active alignment thus requires extensive instrumentation.
Another problem in terminating optical fibers relates to the wide dissimilarities in the myriad connector styles. Because of the different sizes and geometries of connector bodies, ferrules, and other components, any technique adapted for use with one particular connector is generally incompatible with other connector designs. Special adapters kits or jumper cables may be necessary to achieve compatibility.
In light of the foregoing, it would be desirable to devise an improved method of terminating an array of optical fibers to an array of optical devices, which allows for the passive self-alignment of the device array to the optical fiber array. It would be further advantageous if the method accommodated higher interconnection densities, and were generally usable with any commercially available fiber optic connector.
It is therefore one object of the present invention to provide an improved method of interconnecting or terminating a plurality of optical fibers with a plurality of respective active optical devices.
It is another object of the present invention to provide such a method that allows for the passive self-alignment of the optical fibers to the optical devices.
It is yet another object of the present invention to provide highly integrated, low profile fiber optic array transmitters and receivers for ultra-high bandwidth data distribution and communication.
A further object of this approach is to establish a precisely defined interface, with respects to physical separation, between the active (photonic) device apertures and the plurality optical fiber termination. The interface permits a precise uniform physical separation of less than 0.15 mm to be achieved across all emitter and/or detector apertures without physically bonding via an adhesive to the optical fiber connector termination. This reduces the dependency on requiring narrow beam divergence emitters and reduces loss in the detector to fiber termination due to bean divergence.
Still another object is the increase in design flexibility by allowing the optical (emitter/detector) to electrical interface assembly to be pre-fabricated and subsequently inserted into the desired package housing of choice. This eliminates the need for customization when used with commercial optical multi-fiber connectors (ferrules).
Yet another objective is the protective laminate interface between the active emitter/detector and the optical fiber termination. This makes the technique directly applicable to reduced failure risk in harsh environments such as military avionics.
The foregoing objects are achieved in a method of terminating a plurality of optical fibers, generally comprising the steps of placing terminal ends of the optical fibers into a connector to create a fiber end face array, locating a plurality of optical devices on a substrate, the optical devices being arranged in an array having a matching geometry as the fiber end face array, and positioning the connector with respect to the substrate to align the fiber end face array with the optical device array. The optical device substrate can be formed as part of a fiber termination fixture which further includes a carrier having means for aligning the carrier with the multifiber connector. The aligning means can take the form of two holes formed in the carrier and adapted to receive respective alignment pins of the connector. The optical device substrate is advantageously affixed to the carrier by forming a first solder ball contact array pattern on a surface of the optical device substrate, forming a second solder ball contact array pattern on a surface of the carrier, wherein the second solder ball contact array pattern matches the first solder ball contact array pattern, and melting a plurality of solder balls disposed between the first solder ball contact array pattern of the optical device substrate and the second solder ball contact array pattern of the carrier such that solder reflow self-aligns the patterns, and further positions the optical device array in a predetermined orientation with respect to the alignment holes in the carrier. The carrier can be thermally enhanced to act as a heat sink when melting the solder balls. In the illustrative embodiment, the optical devices are active optical devices, such as photodetectors or light emitters. The electrical contacts to the optical devices are made either during or after the chip to carrier attachment. The carrier can include electrical point-to-point connections, which allow optical devices possessing electrical contacts on the device frontside, the device backside, or a combination of frontside and backside contacts, to be used. A housing may be provided to support the fiber termination fixture in a predefined location and orientation with respect to a hole formed in the housing which receives the connector.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.